If you like, you can skip directly to where you can buy this part.
We sell good, original BMW, used Bosch alternator units. The price is $90 plus shipping.
Assuming I’m reading the parts lists the right way, then the official BMW price for the Bosch part is just over $620 plus a core charge of $50.
Various vendors offer the Bosch part. Pelican Parts is my personal favorite. On general principles, I like buying new parts from them. They offer a rebuilt part for just over $250, plus a core charge of $75.
We don’t charge a core charge. Some of the other vendors I’ve researched do add on a core charge. To redeem that, you have to take or send your old part back to where you did the transaction, within a particular span of dates. This seems reasonable — yet often, this ends up being non-viable in practical reality. In such cases, the core charge ends up as simply one more cost.
We could find a remanufactured unit on eBay too, for slightly more than what we are pricing ours at, but there’s a lot of complexity to buying remanufactured units.
No doubt I can also find many made-in-China units, or rebuilt-somewhere unit, but it becomes pretty subtle when one figures out that many of such units do not include the pulley. That means I would have to somehow get the pulley off the old alternator (which isn’t easy, and would probably require a bench vise, which I don’t own) and then putting it on the replacement alternator (which isn’t easy, and would again require a bench vise). It would also require a torque wrench and the specs to which to torque the attaching nut. Many years ago, I attached such a nut too loosely, it came flying off, and the results were not happy. So when I hear “pulley not included” that’s not good news.
I also found a vendor (whom I didn’t recognize) on Amazon, who offers the Bosch part (new or rebuilt, I’m not sure) for just under $170.
It’s probably safe to say that our used units are price-competitive.